Jim Cullen, who teaches at the Ethical Culture Fieldston School in New York, is a book review editor at HNN. His new book, Sensing the Past: Hollywood Stars and Historical Visions, is slated for publication by Oxford University Press later this year. Cullen blogs at American History Now.

The notion that middle age is essentially a cultural construction is not one that will be surprising to historians. But New York Times journalist Patricia Cohen makes this case with breadth and verve. Though it seems to sprawl at times, with a range of opinions that can become tiresome in their predictable diversity -- every opinion about middle age has its rejoinder -- In Our Prime is a serious and useful survey in the subject likely to remain a standard of its kind for some time to come.

Cohen begins by noting that until the twentieth century, there was rarely discussion of what he have come to know as middle age. To the extent that the concept was understood, it was generally regarded as one of productive maturity -- often enviable to the youthful, who longed for the gravitas time conferred. This situation began to change a century ago, heavily influenced by the advent of mass media, particularly movies and advertising, which substantially changed the terms of the equation.

The status of middle age receded still further in the first half of the twentieth century, as psychologists Sigmund Freud and G. Stanley Hall focused on infancy and adolescence as the crucial staging grounds of personal identity. Not until the path-breaking work of Erik Erickson was there much effort to delineate a notion of midlife, and even he backed into via his attempts to segment the either end of a lifetime. Ironically, it was not until the 1960s, in the zenith of youth culture, that there was any real effort to systematically define and trace midlife using longitudinal studies and neurological research backed by serious foundation money. In recent decades these efforts have led to a greater understanding of the the (still imprecisely defined) concept senescence. Current scientific opinion emphasizes the plastic nature of the brain long after maturity, with recent speculation that there are certain kinds of aptitude (like responding to unexpected stress) that older people seem to handle better than younger ones, even if there are not currently good ways to measure a quality that falls into the category of wisdom.

In the last third of the book Cohen surveys "the Midlife Industrial Complex," which she sees as a largely capitalist-driven phenomenon. She notes how a wide array of conditions associated with age, ranging from physical appearance to sexual drive, have been medicalized in recent decades by huckters seeking to exploit the emotional vulnerabilities and relatively deep pockets of Baby Boomers. Yet even this seems to have a silver lining, as marketers are gradually realizing that their mania for the 18-49 demographic overlooks some of the most fertile terrain for their wares. Such a recognition has begun to have an impact on television, for example, where shows geared to more mature and diverse audiences have become more common.

In Our Prime has an even tone and intellectual depth that talks frankly about some of the most dismaying aspects of the aging process. But its overall mood is upbeat: mid-life -- which Cohen resists defining precisely even as the book ends -- is a lengthening time of opportunity. Her message of hope is worth buying, literally and figuratively.